Some fluid ejection systems use heat from thermal resistors to eject fluid drops. For example, thermal inkjet printheads eject fluid ink drops from nozzles by passing electrical current through resistor elements. Heat from a resistor element creates a rapidly expanding vapor bubble that forces a small ink drop out of a firing chamber nozzle. When the resistor element cools, the vapor bubble quickly collapses and draws more fluid ink into the firing chamber in preparation for ejecting another drop from the nozzle. Fluid ink is drawn from a reservoir via a fluid slot that extends through the substrate on which the resistor and chamber are formed.
Improvements in the processes for fabricating fluid slots in fluid ejection devices have lead to narrower fluid slots that reduce device size and improve thermal efficiency. However, the improved processes have also been shown to etch or damage the surface of the resistors. Damage to the surface of the resistor can reduce device lifetime and cause fluid ejection defects (e.g., print defects in an inkjet printing system).
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.